-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Douglas Bates wrote: | On Wed, Mar 19, 2008 at 3:02 PM, Ben Bolker <[EMAIL PROTECTED]> wrote: |> Jean-Baptiste Ferdy <Jean-Baptiste.Ferdy <at> univ-montp2.fr> writes: |> |> > |> > Dear R users, |> > |> > I want to explain binomial data by a serie of fixed effects. My problem is |> > that my binomial data are spatially correlated. Naively, I thought I could |> > found something similar to gls to analyze such data. After some reading, I |> > decided that lmer is probably to tool I need. The model I want to fit would |> > look like |> > |> > lmer ( cbind(n.success,n.failure) ~ (x1 + x2 + ... + xn)^2 , family=binomial, |> > correlation=corExp(1,form=~longitude+latitude)) |> >
| This is more than a notational difference. In a linear model the | effect of b is limited to the linear predictor and, through that, the | mean. The variance-covariance specification can be separated from the | mean and, hence, can be specified separately. It is easy to fool | yourself into thinking that the same should be true for generalized | linear models, just like it is easy to fool yourself into thinking | that all the arguments for the lme function will work unchanged in | lmer. ~ Fair enough. I guess the model I was thinking of was ~ Y ~ Binomial(p,N) ~ logit(p) ~ MVN(mu,Sigma) ~ mu = (determined by model matrix and predictors) ~ Sigma = (exponential spatial correlation matrix)*sigma^2 ~ This model is certainly different from the model that the original poster may have been thinking of, because in the limit where there is no extra-binomial variation, there can't be any correlation either. On the other hand, it seems to be a sensible model. ~ cheers ~ Ben Bolker -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFH4m/zc5UpGjwzenMRAi02AJ9UNy8WsUkN8hVI5ih1yOLxtQn3TwCfeovt Q1iOmczhkWqi4d4VeZDcylo= =Mr7v -----END PGP SIGNATURE----- ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
